From skin to lung: a rare case of PDZRN3/RAF1 fusion in recurrent dermatofibrosarcoma protuberans with lung metastasis.

Dermatofibrosarcoma protuberans (DFSP), a soft tissue neoplasm of intermediate grade not commonly encountered in oncology clinics, has been traditionally known for its locally aggressive nature and recurrence after surgical excision. This spindle cell neoplasm of fibro-histiocytic origin has one of its rare aggressive variants, pronounced by a high risk of local relapse and metastasis, recognized as fibrosarcomatous transformation of dermatofibrosarcoma protuberans (FS-DFSP). Here, we present a novel case of DFSP of the scalp which, after repeated local recurrences, transformed into an aggressive variant (FS-DFSP) with metastasis to the lungs. After comprehensive molecular profiling of the tumor, an infrequent PDZ Domain-Containing RING Finger 3-Rapidly Accelerated Fibrosarcoma 1 (PDZRN3/RAF1) gene fusion was identified, suggesting a plausible targetable chemotherapeutic option in the era of precision medicine. This case report also highlights the diagnostic conundrum faced by medical oncologists and radiologists, who, at first glance, thought of an invasive lung primary malignancy encasing the bronchus, but the histopathological findings turned out to be a flabbergasting surprise.